In 2011, Barclays received a total of 533,047 complaints, of which 281,484 came in the final six months of last year, largely as a result of an increasing number of payment protection insurance (PPI) mis-selling claims.

Lloyds TSB was the country's second most complained to bank, receiving a total of 422,830 complaints last year, of which 240,923 came in the second half, again as a result of rising PPI claims.

Of the 146,316 banking services-related complaints received against Barclays in the second half just over half were upheld in the customer's favour and 96pc were dealt with within eight weeks of being made.

"Complaints are still higher than our customers should expect, but we are on the right track in bringing them down," said Antony Jenkins, chief executive of Barclays global retail and business banking.

A spokesman for Lloyds said that when complaints were considered per 1,000 customers its record compared favourably with other banks. In total it received 1.5 complaints per 1,000 customers, compared with four for Royal Bank of Scotland and NatWest, 3.7 for Barclays, and 4.6 for Santander UK.

Overall, the FSA figures showed a 21pc increase in total industry complaints over the six months between July and December last year, compared to the first half of the year.

However, there are industry concerns that the FSA's figures do not paint an accurate picture of service quality at individual banks. A survey of nine major retail financial services companies by Ernst & Young found industry fears that the complaints figures were being misinterpreted.

"In a hypothetical example, if we compare a firm that applies the full FSA definition, and so only counts complaints that have caused customers 'material distress or inconvenience', to a firm that applies 'any expression of dissatisfaction' throughout the process, the firm using the FSA definition would, in theory, record fewer complaints," said Jenny Clayton at Ernst & Young.

Under FSA rules, regulated firms are required to report any complaints made to them. However, the regulator only publishes the names of those that received more than 500.